Functional regeneration of the optic nerve occurs after injury in lower vertebrates. This regenerative capacity is not observed in the optic nerves of higher vertebrates. This proposal is concerned with the involvement of intermediate filament proteins in the development and regeneration of the optic nerve in the goldfish visual pathway, a system which is particularly amenable for examination. The intermediate filament protein composition of the goldfish visual pathway consists predominantly of a group of four isoelectric variants of 58,000 daltons. The synthesis of two of these proteins occurs in the retina and is linked to optic nerve regeneration. The other two proteins are non-neuronal, are associated with the optic nerve, and show little change in expression during the regeneration process. These proteins are different from the conventional intermediate filament protein composition of the mammalian central nervous system, but may be related to proteins, such as vimentin, which are expressed by mammalian neurons during embryogenesis. Thus, the goldfish intermediate filament proteins may be a molecular link between optic nerve development and regeneration. Molecular cloning techniques will be used to obtain cDNA clones corresponding to the goldfish intermediate filament proteins. Nucleotide sequence analysis of the cDNAs will yield the primary amino acid sequences of these proteins. The structural relationship between the goldfish proteins and vimentin will therefore be determined. The cDNA clones will be used in hybridization studies to determine the number of genes within the goldfish genome which encode for these proteins, the number of different mRNAs produced by these genes, and the differences which exist between unique genes and/or mRNAs; thereby it will be established how, and at what levels, the syntheses of these proteins are regulated. Furthermore, changes in intermediate filament gene expression during the regeneration of the optic nerve will be quantified. In situ hybridization, using the cDNA probes, will determine whether or not molecular heterogeneity exists in the retinal ganglion cell population for these proteins. cDNA probes will also be used in retinal explant studies to determine if tectal factors regulate the synthesis of these proteins. The long term goal of these studies is to understand, at the molecular level, why some visual systems are endowed with the ability to regenerate while other visual systems lack this regenerative capacity.